Method of detinning.



UNITED STATES PATENT OFFICE.

KARL GOLDSCi-IMIDT. AND Jos F WEBER, or ESSEN-ON-THE-RUHR, GERMANY.

METHOD OF-"DETINNlN G.

Essen-on-theRuhr, German Empire, have jointly invented a new and useful method of cleaning able for-being detinned -that is to"say,freed from tinof which the following is an exact specification.

While the scrap of tlnned sheet-iron which results. as Waste material in the manufacture of all kinds of. tin-plate articles has for a long time been technically utilized by being resolved into their components, tin and iron, this has been quite different with the various kinds of articles made from tin-plateyespect;

ally old reserved-food tins, which sofar have seldom een touched by the detinning industry. For more than fifty years numerous patents. relating to the detinmng of tin-plate scrap have been taken out, showing the lively interest t aken in the problem of the utilization of tinned waste materials. These numerous patents, however, nearly exclusively dealt with the problem of separating the tin from the 'iron or otherwise rendering these waste materials suitable for industrial utilization.

But few patents deal with the question of preparing old tin-plate articles for the purpose of rendering same suitable for industrial utilization. Of late patents have been aplied for for machinery forcutting up or pertorating tin-plate'boxes. The most important question, however, of. the cleaning of these tinned materials-using the word cleaning in its widest meaning-has only in exceptional cases formed the subject of patents or of descriptions in the technical literature. With reference to this we refer to the English patent Brindley, No. 8,693, of April 15, 1902, wherein. apparatus are described for melting ofl the solder and for removing from the tinned metal oil, grease, paint, &c. which we call filth.

For the process of freeing metals from tin or detinning, everything that is not tin or iron must be considered as im urity. Thus it is not suflicient to free the ol tinned materials from only lacquer, paper labels, remainders of food, coloring-matter, and Whatever else may still adhere to them from the former contents, or in the form of ornamental or advertising matter, but also the solder, of which Specification ofi Letters Patent.

' A plication filed December 119 sflllifil l old tinned sheetiron boxes and other tinned articles to render the same suit- Patented Nov. 13 ,1906.

much is used in the manufacture of these articles', especlally tin boxes, must be removed, as it contains considerable amounts of lead besides tin. 1 This lead is naturally an impu= rity, since in the various detinning methods in use it combines either with the tin or the tin salts, seriously affecting, of course, the quality of these latter, or else it remains behind in the iron.

A great hindrance to detinning, especially in the-case of old tin boxes, is a thin caoutchouc ring, which in folding the edges of the tins is placed in the fold to make the same tight. All cleaning methods whichdo not destroy this caoutchouc-ring suiier from the drawback that the fold which holds the caoutchouc ring is not attacked by the tindissolving agent. Thus-apart of the tin is not recovered, 'and this part represents not only a loss of tin, but it also makes the iron less valuable on account of its containing tin. The amountJf tin thus lost to the operator is by no means small, considerin that of the 'old tin-plate articles principa ly in question a very large portion consists of old preserved-food tins of medium and small sizesuch as oldsardine-tins, tins for various delicacies, preserves, vegetables, meat, and so onand that of these small tin boxes the folded edge'constitutes a comparatively large percentage. Extensive experiments have shown that tins completely freed from varnish, lacquer, paper, "remainders of'food, and also from the solder, but which still had the strip of caoutchouc in the folds, gave after being detinned an iron containing from 0.5 to one percent. of tin, a quality that is nearly unsalable, because it is useless for the main use of old iron-viz.-, for melting down in the Martin furnace. It has been shown by extensive trials that to render old tinned sheet-iron boxes really serviceable for detinning purposes the cleaning process must be divided in two parts:

First. Removal of the adhering organic substances, not including the above-mentioned caoutchouc strips; Trials have shown that the removal of these organic substances is effected rapidly and with as much comleteness as is required for the purpose 1n view by a treatment of'the old tins with caustic alkali. A dilute solution containin say, three per cent. sodium hydroxid will 0 for the purpose if the solution is heated. One may of course also work with stronger solutionssay with tenper cent. sodium hy droxidwhich may be cold. For reason of economy it will of course generally be preferred to use heated and more diluted solu the solder and the aforementioned caout- These latter being embedded chouc strips. in the air-tight folds. are of course not at all or little affected by the alkaline treatment. By boiling the old tins with soda instead of caustic alkali the effect achieved is by no means equivalent. The treatment with soda requires much'longer time and much stronger solutions, and even then the gun pose aimed at is frequently'not achieve Second. Removal of solder and caoutchouc. If subsequent to the above-described treatment with caustic'alkali the tinned materials be heated to a temperature only slightly above the melting-pointof s0lderfor ex: am le, to about 350 Oelsius the solder wil be gained; but at this low tem erature it will only flow off reluctantly an show a strong tendency of further alloying with the tin. Besides-at this tem eratu-re the caoutchouc strips in thefolds Wlll not be destroyed. To attain this purpose, the tinned materials must be exposed to a temperature decidedly higher than the melting-point of the solder. This presents the advantage not only of the solder beingtobtained in a much more thinly- -liquid state; thus preventing a part of it alloying with the tin on the sheet-iron surface and forming tin-lead alloys, which it is difli-' cult to dissociate and which on their part. again must be considered asagreat hindrance. to the detinning, but also of resulting in the comp.'ete destruction of the caoutchouc strips. The boxes may be heated for a certain length of time to the comparatively low temperature of 400 to 500 Celsius; but a still more, efficient means has been found to be the sudden exposure of the tin boxes to atemperature of from 600 to 800 Celsius. In

this way the solder is melted off in five to.

seven minutes and at the same time the caoutchouc is destroyed. Of course the duration of the heating and the degree of temerature vary according to the size of the tin oxes treatedand mayalso depend on the thickness of the folded edges or on the quality of the caoutchouc to be destroyed, and the above-stated figures are only meant to give an approximate idea and not to repre-.

sent the utmost limits to which one may have to go. Excessive heating must, however, be avoided, because it would cause the tin to alloy with the iron, from which alloy it would not be possible to extract the tin with the methods hitherto known and em loye'd. If, however, the heating is done wit some care, the method described will yield an excellent material, suitable ih every respect for detinning by the electrolytic as well as by a chlorin process. The material shows clean and smooth surfaces. There is only a very small amount formerly occupied by eadadhering, and there are no more inaccessible spots on the material. At the place of the caoutchouc strip there is now a narrow channel, allowing the detinning substance to circulate.

The following is a description of the course of the operation: The old tins are placed in a perforated receptacle, which is provided with a lid similar to that of a wash-cylinder and then dip ed into a vat with heated solution. During the dipping the receptacle containing the tinned materials is stirred, shaken about, or overturned, so that the materials are thoroughly w ashed through withthe lye and-all organic remainders get their share of the treatment. After-thus having removed all organic substances in this manner the cyl-,

inder, with the tinned articles, isplaced in a basin or reservoir filled with water, wherein the materials are washed or rinsed. The cylinder with the tinned articles is then placed in a hearth-furnace, which may be arranged in such manner as to have the fire at the side of the hearth-pit, so that the cylinder susended over the pit will be hit by the passing iire-gases from the side. In this way a rapid heating of the materials in the perforated re-v ceptacle takes lace. The solder flows down and is collected on the hearth. The fire-gases of course escape on the other side of the hearth. In this way the contents of the cylinder can rapidly. be brought to the desired temperature. Subse uently the cylinder, with its contents, is 1%ted out of the-hearth and the contents poured out. This material is then ready for being detinned, either-by the electrolyticprocess or by chlorin orby any other process. 7 1 I As mentioned b Meredith Leitch in his American Patent 0. 800,223, an important item in-the process of preparing old tins for beligg freed from tin is the recovery of the SO er.

The methods of Brindley and Leitch, which i der, suffer from the great drawback that the dried remainders of organic substances, sand and rust, and other impurities drop into the solder, spoilin the same-to suchhn extent as to considerab y reduce its value.

By dividing the operation of cleaning the tins into two parts viz. ,washing of thetinned articles in an alkaline solution and subseguent heatingthe special advantage is insure that the solder (adhering to the tin) is recovered in a state of comparatively high puritythat is to say, free from the remainders of all kinds of impurities adhering to the tins.

Having thus fully described the nature of our invention, what we desire to secure by Letters Patent of the United States is 1. The method of cleaning sheetdron ob jects such as old tin boxes and the like pre paratory to detinning, which consists in first saponifying the adhering filth and afterward exposing the objects to ahigh temperature.

2. The method of cleaning sheet-iron objects such as old tin boxes and the like preparatory to detinning, which consists in first saponiiying the adhering filth by means of an alkaline solution and afterward exposing the objects to a high temperature.

3. The method of cleaning sheet-iron objects such as old tin boxes and the like preparatory to detinning, which consists in first treating them with a solution of sodium hydroxid and afterward exposing them to a high temperature.

4. The method jects such as old tin boxes and the like preparatory to detinning, which consists'in first treating them with a solution of sodium hy- I droxid while in a heated state and afterward exposing them to a high temperature.

5. The method of cleaning sheet-iron objects such as old tin boxes and the like preof cleaning sheet-iron obparatory to detinning, which consistsin lirst 1 treating them with a cleansing solution and afterward exposing them for a certain time to a temperature of not less than 400 and not more than 800 Qelsius, according to the nature of the substances to be deteriorated.

6. The method of cleaning sheet-iron objects such as old tin boxes and the like preparatory to detinning, which consists in first treating them with an alkaline solution and afterward exposing them for a certain time to a temperature of not less than 400 and not morethan 800 Celsius, according to the nature of the substances to be deteriorated.

7. The method of cleaning sheet-iron objects such as old tin boxes and the like, preparatory to detinning, which consists in first treating them with a solution of sodium hydroxid and afterward exposing them for a certain time to a temperature of not less than 400 and not more than 800 Celsius according to the nature of thesubstances to be deteriorated.

8. The method of cleaning sheet-iron objects such as old tin boxes and the like, preparatory to detinning, which consists in first treatingjthem with a solution of sodium hydroxid while in a heated state and afterward exposing them for a certain time to a temperature of not less than 400 and not more than 800 Celsius, according to the nature of the substances to be deteriorated.

inwitncss whereof we have hereunto set our hands in the presence of two witnesses. KARL GOLDSQHMIDT. JUSEF NEBER.

Witnesses PETER Lmnnn, WILLIAM ESSENWEIN. 

